Low back pain (LBP) has a staggeringly negative impact on society in terms of medical expenses and disability. Acute occurrence of LBP results in rapid onset of atrophy of the multifidus muscle, and recurrent LBP is associated with even greater maladaptive changes in trunk extensor muscle morphology and function (i.e., decreased size, strength, and endurance). Rehabilitation strategies for LBP often include resistance training to address these changes in the trunk extensor muscles; however, these exercise protocols are only modestly effective in promoting trunk extensor muscle adaptation as they are generally performed at low-loads (e.g., 25% max strength) that are well below those recommended for muscle adaption (>70% max strength). The use of higher-load trunk exercise is commonly contraindicated because of concern that high spinal compressive loads can cause further injury to the spine. Thus, it is critical to develop therapeutic approaches utilizing low mechanical loads that can still deliver sufficient stimuli to the trunk extensor muscles and reverse the changes in trunk extensor muscle function commonly observed in patients with LBP. Low-load resistance exercise with blood flow restriction (BFR) is an innovative approach for exactly this purpose. This paradigm involves performing exercise with low loads while blood flow to the working muscles is partially occluded by a pressure cuff. We have previously shown that a single bout of BFR exercise increases circulating endocrine growth factors, and we recently completed preliminary studies on chronic BFR exercise training and observed that this modality enhances muscle function without negatively impacting indices of arterial stiffness, nerve conduction, inflammation, and blood coagulation. While this exercise modality cannot be applied directly to the trunk (unfeasible to restrict thorax blood flow), our pilot data indicate a unique cross-transfer effect to the erector spinae muscles when low-load trunk extensor exercise is performed after BFR exercise with the appendicular muscles. Thus performing exercise with the appendicular muscles under BFR prior to low-load exercise with the trunk muscles could enhance muscle size and function without high spinal compressive loads. In this application we propose to conduct an exploratory trial as it relates to determining the effects BFR exercise on erector spinae muscle morphometry and function in patients with recurrent LBP. Our central hypothesis is that BFR exercise with the appendicular muscles performed prior to low-load trunk extensor exercise will produce systemic effects that enhance increases in trunk extensor size, strength, and endurance beyond those seen with only low-load trunk extensor exercise. The potential impact of this work is clear: If effective, this novel exercise modality will provide the foundation for a cost-effective and easy-to-implement rehabilitation strategy that is superior to existing paradigms in its capacity to induce muscle adaptation in the absence of high mechanical and compressive loading on the spine.